Golf balls containing multi-layered cores with heat-activated foam center

ABSTRACT

Multi-layered, golf balls having a core made of a foamed composition are provided. The core preferably has a foam inner core (center) and surrounding thermoset or thermoplastic outer core layer. Preferably, a polyurethane foam composition comprising secondary blowing agents that are activated by heat is used to form the foam center. Non-foamed thermoset materials such as polybutadiene rubber may be used to form the outer core layer. The core layers have different hardness gradients and specific gravity values. The foam cores have good resiliency, thermal stability, and durability over a wide temperature range. The ball further includes a cover that may be multi-layered.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending, co-assigned U.S.patent application Ser. No. 14/982,677 having a filing date of Dec. 29,2015, the disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to multi-layered, golf ballshaving a core made of a foamed composition. Particularly, thedual-layered core has a foam inner core (center) and surroundingthermoset or thermoplastic outer core layer. Preferably, a polyurethanefoam composition comprising secondary blowing agents that are activatedby heat is used to form the foam center. The core layers have differenthardness gradients and specific gravity values. The ball furtherincludes a cover having at least one layer.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including, for example, ethylene acid copolymerionomers, polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable performance properties have contributed to thesemulti-piece balls becoming more popular. Many golf balls used today havemulti-layered cores comprising an inner core and at least onesurrounding outer core layer. For example, the inner core may be made ofa relatively soft and resilient material, while the outer core may bemade of a harder and more rigid material. The “dual-core” sub-assemblyis encapsulated by a cover having at least one layer to provide a finalball assembly. Different materials can be used to manufacture the coreand cover thus imparting desirable properties to the final ball.

In general, dual-cores comprising an inner core (or center) and asurrounding outer core layer are known in the industry. For example,Sugimoto, U.S. Pat. No. 6,390,935 discloses a three-piece golf ballcomprising a core having a center and outer shell and a cover disposedabout the core. The specific gravity of the outer shell is greater thanthe specific gravity of the center. The center has a JIS-C hardness (X)at the center point thereof and a JIS-C hardness (Y) at a surfacethereof satisfying the equation: (Y−X)≥8. The core structure (center andouter shell) has a JIS-C hardness (Z) at a surface of 80 or greater. Thecover has a Shore D hardness of less than 60.

Endo, U.S. Pat. No. 6,520,872 discloses a three-piece golf ballcomprising a center, an intermediate layer formed over the center, and acover formed over the intermediate layer. The center is preferably madeof high-cis polybutadiene rubber; and the intermediate and cover layersare preferably made of an ionomer resin such as an ethylene acidcopolymer.

Watanabe, U.S. Pat. No. 7,160,208 discloses a three-piece golf ballcomprising a rubber-based inner core; a rubber-based outer core layer;and a polyurethane elastomer-based cover. The inner core layer has aJIS-C hardness of 50 to 85; the outer core layer has a JIS-C hardness of70 to 90; and the cover has a Shore D hardness of 46 to 55. Also, theinner core has a specific gravity of more than 1.0, and the core outerlayer has a specific gravity equal to or greater than that of that ofthe inner core.

The core sub-structure located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance versusballs with low COR values. These properties are particularly importantfor long distance shots. For example, balls having high resiliency andCOR values tend to travel a relatively far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif the ball is hooked or sliced. Meanwhile, the “feel” of the ballgenerally refers to the sensation that a player experiences whenstriking the ball with the club and it is a difficult property toquantify. Most players prefer balls having a soft feel, because theplayer experience a more natural and comfortable sensation when theirclub face makes contact with these balls. Balls having a softer feel areparticularly desirable when making short shots around the green, becausethe player senses more with such balls. The feel of the ball primarilydepends upon the hardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials for improving the playing performance and other properties ofthe ball. For example, golf balls containing cores made from foamcompositions are generally known in the industry. Puckett and Cadorniga,U.S. Pat. Nos. 4,836,552 and 4,839,116 disclose one-piece, shortdistance golf balls made of a foam composition comprising athermoplastic polymer (ethylene acid copolymer ionomer such as Surlyn®)and filler material (microscopic glass bubbles). The density of thecomposition increases from the center to the surface of the ball. Thus,the ball has relatively dense outer skin and a cellular inner core.According to the '552 and '116 patents, by providing a short distancegolf ball, which will play approximately 50% of the distance of aconventional golf ball, the land requirements for a golf course can bereduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece golf ball(FIG. 2) containing a high density center (3) made of steel, surroundedby an outer core (4) of low density resilient syntactic foamcomposition, and encapsulated by an ethylene acid copolymer ionomer(Surlyn®) cover (5). The '126 patent defines the syntactic foam as beinga low density composition consisting of granulated cork or hollowspheres of either phenolic, epoxy, ceramic or glass, dispersed within aresilient elastomer.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprising an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.Alternatively, the compressible material may be dispersed throughout theentire core. In one embodiment, the core comprises an inner and outerportion. In another embodiment, the core comprises inner and outerlayers.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core, optional intermediate layer, andhigh specific gravity cover with Shore D hardness in the range of about40 to about 80. The core is preferably made from a highly neutralizedthermoplastic polymer such as ethylene acid copolymer which has beenfoamed.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

Although some foam core constructions for golf balls have beenconsidered over the years, there are drawbacks with using some foammaterials. For example, one drawback is that the foam center (innercore) can be exposed to high temperatures during the manufacturingprocess. These conditions can cause melting of the foam centers andvarious other problems including, for example, skinning of the centersurface, partial or total collapse of the foam, increased density, andcenter size reduction. Another drawback is that some polyurethane foamscan lose their elasticity as the temperature changes. Other propertiesof these foam compositions also may degrade when exposed to coldertemperatures. Golf ball cores are exposed to a wide range of high andlow temperatures during their life span. If the chemical and physicalproperties of the foam composition change, the properties of theresulting golf ball core may be adversely affected. For example, theremay be a negative impact on the size, resiliency, and hardness of thefoam core.

In view of some of the disadvantages with some foam compositions, itwould be desirable to have new foam compositions and manufacturingmethods for making foam core constructions. The foam compositions shouldhave good stability. The resulting foam cores also should have goodresiliency (rebounding performance), thermal stability, and durabilityover a wide temperature range. The manufacturing methods shouldeffectively produce uniformly-sized cores that are durable and will notdeteriorate. The present invention provides new foam core compositions,core constructions, and manufacturing methods having such advantageousfeatures and other benefits. The invention also encompasses golf ballscontaining the improved core assemblies.

SUMMARY OF THE INVENTION

The present invention provides a golf ball comprising a core assemblyand cover. The golf ball comprises an inner core layer comprising asecondary heat-activated foam composition. The inner core layer has adiameter in the range of about 0.100 to about 1.100 inches, preferablyabout 0.100 to about 0.900 inches; and a specific gravity (SG_(inner))and a center hardness (H_(inner core center)), and ii) an outer corelayer comprising a non-foamed thermoset rubber composition, wherein theouter core layer is disposed about the inner core and has a thickness inthe range of about 0.100 to about 0.750 inches, preferably about 0.250to about 0.750 inches, and a specific gravity (SG_(outer)) an outersurface hardness (H_(outer surface of OC)). Preferably, the SG_(outer)is greater than the SG_(inner),

In one version, the (H_(inner core center)) is preferably in the rangeof about 10 to about 60 Shore C and the (H_(outer surface of OC)) ispreferably in the range of about 65 to about 96 Shore C to provide apositive hardness gradient across the core assembly. In another version,the H_(inner core center) is in the range of about 10 to about 60 ShoreC and the H_(outer surface of OC) is in the range of about 45 to about96 Shore C.

The secondary heat-activated foam composition preferably comprisesprimary and secondary chemical blowing agents. Water may be used as theprimary blowing agent. Suitable secondary blowing agents include, forexample, azo, nitroso, hydrazine, carbazide, and hydrogen carbonatecompounds, and mixtures thereof. Preferably, the secondary blowing agentis 4, 4′-oxybis(benzenesulfonylhydrazide) or sodium hydrogen carbonate.

The method of this invention involves charging the polymer materials,blowing agent, and any optional ingredients (for example, fillers) tothe mold. The composition is treated with sufficient heat and pressureand the primary blowing agents are activated, causing the polymermixture to foam. The secondary blowing agents are activated in a secondmolding step when the outer core layer is molded over the inner core. Inone embodiment, the composition may further comprise expandablegas-containing microspheres.

Thermoset or thermoplastic materials are used to form the foamed innercore, and preferably a foamed polyurethane inner core is formed. Thefoamed polyurethane may be prepared by adding water in a sufficientamount to cause the mixture to foam, and a secondary chemical blowingagent to a mixture of polyisocyanates, polyols, curing agents,surfactants, and catalysts. Non-foamed thermoset or thermoplasticmaterials also may be used to form the outer core layer. Preferably, athermoset rubber material such as polybutadiene rubber is used. Thus, inone embodiment, the dual-core includes a foam inner core (center) and asurrounding non-foamed thermoset core layer that is preferably made frompolybutadiene rubber. In another embodiment, the dual-core includes afoam inner core (center) and a surrounding non-foamed thermoplastic corelayer. For example, partially or highly neutralized olefin acidcopolymers or non-ionomeric polymers may be used.

The core layers may have different specific gravity levels. For example,the inner core layer may have a diameter in the range of about 0.100 toabout 0.900 inches, or 0.400 to 0.800 inches, and a specific gravity inthe range of about 0.25 to about 1.25 g/cc or 0.30 to 0.95 g/cc. In oneversion, the outer core layer has a thickness in the range of about0.250 to about 0.750 inches and a specific gravity in the range of about0.60 to about 2.90 g/cc.

The core layers also may have different hardness gradients. For example,each core layer may have a positive, zero, or negative hardnessgradient. In a first embodiment, the inner core has a positive hardnessgradient; and the outer core layer has a positive hardness gradient. Ina second embodiment, the inner core has a zero or negative hardnessgradient; and the outer core layer has a positive hardness gradient. Inyet another embodiment, the inner core has a positive hardness gradient,and the outer core layer has zero or negative hardness gradient. Instill another version, both the inner and outer core layers have zero ornegative hardness gradients.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a spherical inner core made of a foamedcomposition in accordance with the present invention;

FIG. 2 is a perspective view of one embodiment of upper and lower moldcavities used to make the inner core of the present invention;

FIG. 3 is a perspective view of a spherical inner core made of a foamedcomposition and two half-shells made of a thermoset rubber compositionin accordance with the present invention;

FIG. 3A is a perspective view of one embodiment of upper and lower moldcavities used to mold the outer core layer so that it encapsulates theinner core of FIG. 3 in accordance with the present invention;

FIG. 4 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 5 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention; and

FIG. 6 is a perspective view of a finished golf ball having a dimpledcover made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a three-piece golf ballcontaining a dual-layered core and single-layered cover is made. Thedual-core includes an inner core (center) and surrounding outer corelayer. In another version, a four-piece golf ball containing a dual-coreand dual-cover (inner cover and outer cover layers) is made. In yetanother construction, a four-piece or five-piece golf ball containing adual-core; casing layer(s); and cover layer(s) may be made. As usedherein, the term, “casing layer” means a layer of the ball disposedbetween the multi-layered core sub-assembly and cover. The casing layeralso may be referred to as a mantle or intermediate layer. The diameterand thickness of the different layers along with properties such ashardness and compression may vary depending upon the construction anddesired playing performance properties of the golf ball.

Inner Core Composition

Preferably, the golf balls of this invention contain a core structurecomprising an inner core (center) and surrounding outer core layer. Inthe present invention, “secondary heat-activated foam compositions,” areused to prepare the inner core (center) structure of this invention. Bythe term, “secondary heat-activated foam compositions,” as used herein,it is meant foam materials containing secondary chemical blowing agentsthat are activated during over-molding of the foam center with athermoset rubber outer core layer composition.

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition having either an openor closed cellular structure. Flexible foams generally have an open cellstructure, where the cells walls are incomplete and contain small holesthrough which liquid and air can permeate. Rigid foams generally have aclosed cell structure, where the cell walls are continuous and complete.Many foams contain both open and closed cells. It also is possible toformulate flexible foams having a closed cell structure and likewise toformulate rigid foams having an open cell structure. Variousthermoplastic and thermoset materials may be used in forming the foamcompositions of this invention as discussed further below. In onepreferred embodiment, a polyurethane foam composition is prepared.

The foaming (blowing) agents used to form the foam are typically are inthe form of powder, pellets, or liquids and they are added to thecomposition, where they decompose or react during heating and generategaseous by-products (for example, nitrogen or carbon dioxide). The gasis dispersed and trapped throughout the composition and foams it. Forexample, water may be used as the foaming agent. Air bubbles areintroduced into the mixture of the isocyanate and polyol compounds andwater by high-speed mixing equipment. As discussed in more detailfurther below, the isocyanates react with the water to generate carbondioxide which fills and expands the cells created during the mixingprocess.

The chemical foaming agents may be inorganic, such as ammonium carbonateand carbonates of alkalai metals, or may be organic, such as azo anddiazo compounds, such as nitrogen-based azo compounds. Suitable azocompounds include, but are not limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), and azodicarbonamide. Other compoundsinclude, for example, p,p′-oxybis(benzene sulfonyl hydrazide), p-toluenesulfonyl semicarbazide, and p-toluene sulfonyl hydrazide. Other foamingagents include any of the Celogens® sold by Crompton ChemicalCorporation, and nitroso compounds, sulfonylhydrazides, azides oforganic acids and their analogs, triazines, tri- and tetrazolederivatives, sulfonyl semicarbazides, urea derivatives, guanidinederivatives, and esters such as alkoxyboroxines. Also, foaming agentsthat liberate gasses as a result of chemical interaction betweencomponents such as mixtures of acids and metals, mixtures of organicacids and inorganic carbonates, mixtures of nitriles and ammonium salts,and the hydrolytic decomposition of urea may be used. In the presentinvention, the foam composition preferably is formed from primary andsecondary chemical blowing agents.

Primary Chemical Blowing Agents—

One or more primary chemical blowing agents are added to the formulationthat will be foamed. Water is a preferred blowing agent. When added tothe polyurethane formulation, water will react with the isocyanategroups and form carbamic acid intermediates. The carbamic acids readilydecarboxylate to form an amine and carbon dioxide. The newly formedamine can then further react with other isocyanate groups to form urealinkages and the carbon dioxide forms the bubbles to produce the foam.The water is added in a sufficient amount to cause the mixture to foam.In one preferred embodiment, the water is present in the composition inan amount in the range of 0.25 to 3.0% by weight based on total weightof the composition.

Physical Blowing Agents—

The physical blowing agents are different materials and have differentworking mechanisms than the chemical blowing agents. The physicalblowing agents may be used, in addition to or as an alternative to, theprimary chemical blowing agents. These blowing agents typically aregasses that are introduced under high pressure directly into the polymercomposition. Chlorofluorocarbons (CFCs) and partially halogenatedchlorofluorocarbons are effective, but these compounds are banned inmany countries because of their environmental side effects.Alternatively, aliphatic and cyclic hydrocarbon gasses such as isobuteneand pentane may be used. Inert gasses, such as carbon dioxide andnitrogen, also are suitable. With physical blowing agents, theisocyanate and polyol compounds react to form polyurethane linkages andthe reaction generates heat. Foam cells are generated and as the foamingagent vaporizes, the gas becomes trapped in the cells of the foam.

Secondary Chemical Blowing Agents—

In the present invention, one or more secondary chemical blowing agentsare preferably added to the formulation that will be foamed. Thus, inone preferred version, the formulation contains a blend of primary andsecondary blowing agents. As discussed above, the blend of primary andsecondary blowing agents also may contain one or more physical blowingagents. In another embodiment, the formulation contains a blend ofphysical blowing agents and secondary blowing agents. The secondaryblowing agents are not activated during initial molding of the foamcenter. Instead, these secondary blowing agents are activated during themolding of the outer core layer onto the inner core. In one preferredembodiment, the secondary blowing agent is present in the composition inan amount in the range of 0.1 to 5.0% by weight based on total weight ofthe composition, and more preferably in the range of 0.5 to 3.0%.

The secondary blowing agents may be selected, for example, from thegroup consisting of azo compounds such as azodicarbonamide (ADCA) andazobisformamide; nitroso compounds such as N, N-dimethyl-N, N-dinitrosoterephthalamide, N, N-dinitroso-pentamethylene-tetramine (DPT), and5-Phenyltetrazole (5 PT); hydrazine derivatives such as 4,4′-Oxybis(benzenesulfonylhydrazide) (OBSH), hydrazodicarbonamide (HDCA),toluenesulfonyl hydrazide (TSH), and benzene-sulfonyl-hydrazide (BSH),carbazide compounds such as toluenesulfonyl-semicarbazide (TSH); andhydrogen carbonates such as sodium hydrogen carbonate (NaHCO₃); andmixtures thereof. Thus, the formulation may contain a mixture ofsecondary blowing agents.

In one preferred embodiment, chemical blowing agents having relativelylow decomposition temperatures that complement the heating temperaturesin the molding cycle are used. These blowing agents will start todecompose as the designated temperature in the molding process, and thefoaming reaction will proceed more quickly. For example, the secondaryblowing may be selected from the group consisting of OBSH, having adecomposition temperature of about 160° C. and NaHCO₃ having adecomposition temperature of about 150° C. These blowing agents arecommercially available from such companies as Tramaco, GmbH (Pinneberg,Germany) and Eiwa Chemical Ind. Co., Ltd. (Mitsubishi Gas ChemicalAmerica, Inc., Detroit, Mich.).

It is recognized that during the decomposition reaction of certainchemical foaming agents, more heat and energy is released than is neededfor the reaction. Once the decomposition has started, it continues for arelatively long time period. If these foaming agents are used, longercooling periods are generally required. Hydrazide and azo-basedcompounds often are used as exothermic foaming agents. On the otherhand, endothermic foaming agents need energy for decomposition. Thus,the release of the gasses quickly stops after the supply of heat to thecomposition has been terminated. If the composition is produced usingthese foaming agents, shorter cooling periods are needed. Bicarbonateand citric acid-based foaming agents can be used as exothermic foamingagents.

Additional Blowing Agents—

Other suitable blowing agents that may be added to the formulation thatwill be foamed in accordance with this invention include, for example,expandable gas-containing microspheres. Exemplary microspheres consistof an acrylonitrile polymer shell encapsulating a volatile gas, such asisopentane gas. This gas is contained within the sphere as a blowingagent. In their unexpanded state, the diameter of these hollow spheresrange from 10 to 17 μm and have a true density of 1000 to 1300 kg/m³.When heated, the gas inside the shell increases its pressure and thethermoplastic shell softens, resulting in a dramatic increase of thevolume of the microspheres. Fully expanded, the volume of themicrospheres will increase more than 40 times (typical diameter valueswould be an increase from 10 to 40 μm), resulting in a true densitybelow 30 kg/m³ (0.25 lbs/gallon). Typical expansion temperatures rangefrom 80-190° C. (176-374° F.). Such expandable microspheres arecommercially available as Expancel® from Expancel of Sweden or AkzoNobel.

In the process of this invention, the materials used to prepare the foamare charged to the mold for producing the inner core. The mold may beequipped with steam nozzles so that steam can be injected into the moldcavity. The temperature inside of the mold can vary, for example, thetemperature can range from about 80° C. to about 400° C. Steam, hot air,hot water, or radiant heat may be used to foam the composition. Thecomposition expands as it is heated. The temperature must be chosencarefully and must be sufficiently high so that it activates the primaryblowing agents and foams the mixture, but it must not be excessivelyhigh so that it activates the secondary blowing agents. In general, thetemperature should be in the range of about room temperature (RT) toabout 180° F. and preferably in the range of about room temperature (RT)to about 150° F. so that it activates the primary blowing agents. Oncethe polymer materials, blowing agent, and any optional ingredients (forexample, fillers) are charged to the mold and treated with sufficientheat and pressure, the primary blowing agents are activated. This causesthe polymer mixture to foam and form the primary heat-activated foamcomposition in the mold. The primary heat-activated foam compositionfurther contains secondary blowing agents that are not activated duringthis initial molding step. Rather, these secondary blowing agents areactivated in a second molding step when the outer core layer is moldedover the inner core as discussed further below.

Foam Polymers.

As discussed above, polyurethane foam is preferably prepared inaccordance with this invention. It is recognized, however, that a widevariety of thermoplastic and thermoset materials may be used in formingthe foam compositions of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® 10 ionomers of ethylene acrylicacid copolymers, commercially available from Dow Chemical Company; andClarix® ionomer resins, commercially available from A. Schulman Inc.);polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, commercially available from ArkemaInc; cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof.

Castable polyurethanes, polyureas, and hybrids ofpolyurethanes-polyureas are particularly desirable because thesematerials can be used to make a golf ball having good playingperformance properties as discussed further below. By the term, “hybridsof polyurethane and polyurea,” it is meant to include copolymers andblends thereof. Basically, polyurethane compositions contain urethanelinkages formed by the reaction of a multi-functional isocyanatecontaining two or more NCO groups with a polyol having two or morehydroxyl groups (OH—OH) sometimes in the presence of a catalyst andother additives. Generally, polyurethanes can be produced in asingle-step reaction (one-shot) or in a two-step reaction via aprepolymer or quasi-prepolymer. In the one-shot method, all of thecomponents are combined at once, that is, all of the raw ingredients areadded to a reaction vessel, and the reaction is allowed to take place.In the prepolymer method, an excess of polyisocyanate is first reactedwith some amount of a polyol to form the prepolymer which containsreactive NCO groups. This prepolymer is then reacted again with a chainextender or curing agent polyol to form the final polyurethane. Polyureacompositions, which are distinct from the above-described polyurethanes,also can be formed. In general, polyurea compositions contain urealinkages formed by reacting an isocyanate group (—N═C═O) with an aminegroup (NH or NH₂). Polyureas can be produced in similar fashion topolyurethanes by either a one shot or prepolymer method. In forming apolyurea polymer, the polyol would be substituted with a suitablepolyamine. Hybrid compositions containing urethane and urea linkagesalso may be produced. For example, when polyurethane prepolymer isreacted with amine-terminated curing agents during the chain-extendingstep, any excess isocyanate groups in the prepolymer will react with theamine groups in the curing agent. The resulting polyurethane-ureacomposition contains urethane and urea linkages and may be referred toas a hybrid. In another example, a hybrid composition may be producedwhen a polyurea prepolymer is reacted with a hydroxyl-terminated curingagent. A wide variety of isocyanates, polyols, polyamines, and curingagents can be used to form the polyurethane and polyurea compositions asdiscussed further below.

More particularly, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediolsuch, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3′-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines, 3,3′,5,5‘-tetraethyl-4,4’-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, fillers,cross-linking agents, chain extenders, surfactants, dyes and pigments,coloring agents, fluorescent agents, adsorbents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Fillers.

The foam composition may contain fillers such as, for example, mineralfiller particulate. Suitable mineral filler particulates includecompounds such as zinc oxide, limestone, silica, mica, barytes,lithopone, zinc sulfide, talc, calcium carbonate, magnesium carbonate,clays, powdered metals and alloys such as bismuth, brass, bronze,cobalt, copper, iron, nickel, tungsten, aluminum, tin, precipitatedhydrated silica, fumed silica, mica, calcium metasilicate, bariumsulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, carbonates such as calcium or magnesium or bariumcarbonate, sulfates such as calcium or magnesium or barium sulfate.Silicon dioxides are particularly preferred because they are based onSi—O bonds and these material are compatible with the Si—O—Si backboneof the silicone foam. Adding fillers to the composition provides manybenefits including helping improve the stiffness and strength of thecomposition. The mineral fillers tend to help decrease the size of thefoam cells and increase cell density. The mineral fillers also tend tohelp improve the physical properties of the foam such as hardness,compression set, and tensile strength.

More particularly, clay particulate fillers, such as Garamite® mixedmineral thixotropes and Cloisite® and Nanofil® nanoclays, commerciallyavailable from Southern Clay Products, Inc., and Nanomax® and Nanomer®nanoclays, commercially available from Nanocor, Inc may be used. Othernano-scale materials such as nanotubes and nanoflakes also may be used.Also, talc particulate (e.g., Luzenac HAR® high aspect ratio talcs,commercially available from Luzenac America, Inc.), glass (e.g., glassflake, milled glass, and microglass), and combinations thereof may beused. Metal oxide fillers have good heat-stability and include, forexample, aluminum oxide, zinc oxide, tin oxide, barium sulfate, zincsulfate, calcium oxide, calcium carbonate, zinc carbonate, bariumcarbonate, tungsten, tungsten carbide, and lead silicate fillers. Thesemetal oxides and other metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof may be added to the silicone foam composition.

Surfactants.

The foam composition also may contain surfactants to stabilize the foamand help control the foam cell size and structure. In one preferredversion, the foam composition includes silicone surfactant. In general,the surfactant helps regulate the foam cell size and stabilizes the cellwalls to prevent the cells from collapsing. As discussed above, theliquid reactants tend to react rapidly to form the foam. The “liquid”foam develops into a solid silicone foam in a relatively short period oftime. If a silicone or other surfactant is not added, the gas-liquidinterface between the liquid reactants and expanding gas bubbles may notsupport the stress. As a result, the cell window can crack or ruptureand there can be cell wall drainage. In turn, the foam can collapse onitself. Adding a surfactant helps create a surface tension gradientalong the gas-liquid interface and helps reduce cell wall drainage. Thesurfactant has a relatively low surface tension and thus can lower thesurface tension of the foam. It is believed the surfactant orientsitself the foam cell walls and lowers the surface tension to create thesurface tension gradient. Blowing efficiency and nucleation aresupported by adding the surfactant and thus more bubbles are created inthe system. The surfactant also helps create a greater number of smallersized foam cells and increases the closed cell content of the foam duethe surfactant's lower surface tension. Thus, the cell structure in thefoam is maintained as the as gas is prevented from diffusing out throughthe cell walls. Along with the decrease in cell size, there is adecrease in thermal conductivity. The resulting foam material tends tohave greater compression strength and modulus. This may be due to theincrease in closed cell content and smaller cell size.

As discussed further below, in one preferred embodiment, the specificgravity (density) of the foam inner core is less than the specificgravity of the outer core. If an excess amount of mineral filler orother additives are included in the foam composition, they should not beadded in an amount that would increase the specific gravity (density) ofthe foam inner core to a level such that it would be greater than thespecific gravity of the outer core layer. If the ball's mass isconcentrated towards the outer surface (for example, outer core layers),and the outer core layer has a higher specific gravity than the innercore, the ball has a relatively high Moment of Inertia (MOI). In suchballs, most of the mass is located away from the ball's axis of rotationand thus more force is needed to generate spin. These balls have agenerally low spin rate as the ball leaves the club's face after contactbetween the ball and club. Such core structures (wherein the specificgravity of the outer core is greater than the specific gravity of theinner core) are preferred in the present invention. Thus, in onepreferred embodiment, the concentration of mineral filler particulate inthe foam composition is in the range of about 0.1 to about 9.0% byweight.

Outer Core Composition

As discussed above, the inner core (center) is made preferably from afoamed polyurethane composition. Preferably, a two-layered or dual-coreis made, wherein the inner core is surrounded by an outer core layer. Inone preferred embodiment, the outer core layer is formed from anon-foamed thermoset composition and more preferably from a non-foamedthermoset rubber composition.

Suitable thermoset rubber materials that may be used to form the outercore layer include, but are not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

In the present invention, the inner core (center) comprises a foamthermoplastic or thermoset polymer composition that may be preparedusing the above-described methods. Preferably, the center comprises apolyurethane foam composition. The foam may have an open or closedcellular structure or combinations thereof and may range from relativelyrigid foam to very flexible foam. Referring to FIG. 1, a foamed innercore (4) having a geometric center (6) and outer skin (8) may beprepared in accordance with this invention.

As discussed above, the inner core structure is prepared from asecondary heat-activated foam composition. Referring to FIG. 2, oneversion of a mold for preparing the foamed inner core is shown. The moldincludes lower and upper mold cavities (9, 10) that are placed in lowerand upper mold frame plates (11, 12). The frame plates (11, 12) containguide pins and complementary alignment holes (not shown in drawing). Theguide pins are inserted into the alignment holes to secure the lowerplate (11) to the upper plate (12). The lower and upper mold cavities(9, 10) are mated together as the frame plates (11, 12) are fastened.When the lower and upper mold cavities (9, 10) are joined together, theydefine an interior spherical cavity that houses the spherical core. Theupper mold contains a vent or hole (14) to allow for the expanding foamto fill the cavities uniformly. A secondary overflow chamber (16), whichis located above the vent (14), can be used to adjust the amount of foamoverflow and thus adjust the density of the core structure being moldedin the cavities. As the lower and upper mold cavities (9, 10) are matedtogether and sufficient heat and pressure is applied, the particles fusetogether, cure and solidify to form a relatively rigid or flexible andlightweight spherical core. The resulting cores are cooled and thenremoved from the mold.

Meanwhile, the outer core layer is prepared by an over-molding process,wherein the outer core layer (preferably a non-foamed thermoset rubbercomposition) is molded over the inner core. The outer core layer may bemolded over the foamed inner core using a variety of molding techniques.

For example, the outer core composition (preferably a thermoset rubbercomposition as described above) may be injection-molded orcompression-molded to produce half-shells. These smooth-surfacedhemispherical shells are then placed around the foamed, spherical innercore in a compression mold. Under sufficient heating and pressure, theshells fuse together to form an outer core layer that encapsulates thefoamed inner core. More particularly, as shown in FIGS. 3 and 3A, afterthe two half-shells (17 a 17 b) made from a rubber or other compositionhave been prepared, they are joined together in a mold to encase thepreviously molded inner core (4). The hemispherical shells (17 a, 17 b)and inner core (4) are placed in a mold between a first mold member (17a) and a second mold member (17 b). The first and second mold members(19, 19) are subsequently pressed together to join together thehalf-shells (17 a, 17 b) under sufficient hat and pressure. This moldingprocess forms the outer core layer. As a result, a finished coreassembly (inner core and surrounding outer core layer) is produced.

In another method, the outer core composition may be added to aninjection-molding machine. After the foamed inner core has beenpositioned properly in the injection-molding cavity, the outer corecomposition is injection-molded directly over the inner core. In yetanother method, the outer core layer may be formed bycompression-molding the outer core composition directly around the innercore.

During the over-molding of the foamed center with the thermoset rubberouter core layer composition, the heat used in the curing stage of themolding cycle activates/decomposes the secondary chemical blowing agent.This step releases a sufficient quantity of gaseous by-product (forexample CO₂ or nitrogen) to maintain and preserve the size, density andcell structure of the foam core. As discussed above, the secondaryblowing agents can be endothermic or exothermic, and can be used solelyor in various combinations. Different secondary blowing agents areavailable with many different decomposition temperatures. Selection ofthe appropriate secondary blowing agent is determined by coordinatingthe molding cycle temperature and time period from the start of thecycle to the decomposition temperature of the blowing agent(s). Inaddition, other catalysts can be used to accelerate decomposition ofblowing agent. One drawback with conventional core constructions havinga foam center and surrounding thermoset rubber outer core layer is thatfoam centers can undergo significant changes in physical properties whensubjected to temperatures and pressures outside their design criteria.In some instances, the foam centers can actually melt and soften. Forexample, in standard manufacturing operations, during molding of therubber outer-core layers, mold temperatures in excess of 300° F. areused for heat cycles of 15 minutes or longer, along with significantcompressive forces. Additionally, the interior of the outer core can seea substantial spike in temperature due to the chemical exothermicreaction that occurs as the cross-linking peroxides decompose. This cancause melting of the foam centers and lead to various problems includingskinning of the center surface, partial or total collapse of the foam,increased density, and center size reduction.

As discussed above, the present invention overcomes these drawbacks byusing secondary heat-activated foam compositions in the manufacturing ofthe core structure. The foam materials contain secondary chemicalblowing agents that are activated during over-molding of the foam centerwith a thermoset rubber outer core layer composition. In the presentinvention, the foam composition is preferably formed from primary andsecondary chemical blowing agents. One or more primary chemical blowingagents are added to the inner core formulation that will be foamed.Water is a preferred primary chemical blowing agent. When added to thepolyurethane formulation, water will react with the isocyanate groupsand form carbamic acid intermediates. The carbamic acids readilydecarboxylate to form an amine and carbon dioxide. The newly formedamine can then further react with other isocyanate groups to form urealinkages and the carbon dioxide forms the bubbles to produce the foam.One or more secondary chemical blowing agents also are added to theformulation that will be foamed. These secondary blowing agents are notactivated during initial molding of the foam center. Instead, thesesecondary blowing agents are activated during the molding of the outercore layer onto the inner core.

The materials used to prepare the foam are charged to the mold forproducing the inner core. The mold may be equipped with steam nozzles sothat steam can be injected into the mold cavity. The temperature insideof the mold can vary, for example, the temperature can range from about80° C. to about 400° C. Steam, hot air, hot water, or radiant heat maybe used to foam the composition. The composition expands as it isheated. The temperature must be chosen carefully and must besufficiently high so that it activates the primary blowing agents andfoams the mixture, but it must not be excessively high so that itactivates the secondary blowing agents. In general, the temperatureshould be in the range of about 80° C. to about 250° C. and preferablyin the range of about 90° C. to about 220° C. so that it activates theprimary blowing agents. Once the polymer materials, blowing agent, andany optional ingredients (for example, fillers) are charged to the moldand treated with sufficient heat and pressure, the primary blowingagents are activated. This causes the polymer mixture to foam and formthe primary heat-activated foam composition in the mold. The primaryheat-activated foam composition further contains secondary blowingagents that are not activated during this initial molding step. Rather,these secondary blowing agents are activated in a second molding stepwhen the outer core layer is molded over the inner core as discussedfurther below. This process helps maintain and preserve the size,density and cell structure of the foam core.

Properties of Foams

The foam compositions of this invention have numerous chemical andphysical properties making them suitable for core assemblies in golfballs.

The density of the foam is an important property and is defines as theweight per unit volume (typically, g/cm³) and can be measured per ASTMD-1622. The hardness, stiffness, and load-bearing capacity of the foamare independent of the foam's density, although foams having a highdensity typically have high hardness and stiffness. Normally, foamshaving higher densities have higher compression strength. Surprisingly,the foam compositions used to produce the inner core of the golf ballsper this invention have a relatively low density; however, the foams arenot necessarily soft and flexible, rather, they may be relatively firm,rigid, or semi-rigid depending upon the desired golf ball properties.Tensile strength, tear-resistance, and elongation generally refer to thefoam's ability to resist breaking or tearing, and these properties canbe measured per ASTM D-1623. The durability of foams is important,because introducing fillers and other additives into the foamcomposition can increase the tendency of the foam to break or tearapart. In general, the tensile strength of the foam compositions of thisinvention is in the range of about 20 to about 1000 psi (parallel to thefoam rise) and about 50 to about 1000 psi (perpendicular to the foamrise) as measured per ASTM D-1623 at 23° C. and 50% relative humidity(RH). Meanwhile, the flex modulus of the foams of this invention isgenerally in the range of about 5 to about 45 kPa as measured per ASTMD-790, and the foams generally have a compressive modulus of 200 to50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required to compress theblock by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

Hardness of the Inner Core

As shown in FIG. 1, a foamed inner core (4) having a geometric center(6) and outer skin (8) may be prepared per the molding method discussedabove. The outer skin (8) is generally a non-foamed region that formsthe outer surface of the core structure. As discussed above, in onemethod of this invention, pre-formed polyurethane foam particles areformed and these particles are coated with a heat-activatable binder. Inanother method, the foam particles are not coated with a binder. Theseuncoated particles are heat-treated and the particles are pressedtogether. Because the outer skin (8) of the particles is normally anon-foamed region, the adjacent particles can fuse together more easily.The non-foamed outer skin (8) also helps the particles to bond to eachother when the particles are coated with a heat-activated binder.

The resulting inner core preferably has a diameter within a range ofabout 0.100 to about 1.100 inches. For example, the inner core may havea diameter within a range of about 0.250 to about 1.000 inches. Inanother example, the inner core may have a diameter within a range ofabout 0.300 to about 0.800 inches. More particularly, the inner corepreferably has a diameter size with a lower limit of about 0.10 or 0.12or 0.15 or 0.17 or 0.25 or 0.30 or 0.35 or 0.38 or 0.45 or 0.50 or 0.52or 0.55 inches and an upper limit of about 0.60 or 0.63 or 0.65 or 0.70or 0.74 or 0.80 or 0.86 or 0.90 or 0.95 or 1.00 or 1.02 or 1.10 inches.The outer skin (8) of the inner core is relatively thin preferablyhaving a thickness of less than about 0.020 inches and more preferablyless than 0.010 inches. In one preferred embodiment, the foamed core hasa “positive” hardness gradient (that is, the outer skin of the innercore is harder than its geometric center.)

For example, the geometric center hardness of the inner core(H_(inner core center)), as measured in Shore C units, may be about 10Shore C or greater and preferably has a lower limit of about 10 or 13 or16 or 20 or 25 or 30 or 32 or 34 or 36 or 40 Shore C and an upper limitof about 42 or 44 or 48 or 50 or 52 or 56 or 60 or 62 or 65 or 68 or 70or 74 or 78 or 80 or 84 or 90 Shore C. In one preferred version, thegeometric center hardness of the inner core (H_(inner core center)) isabout 40 Shore C.

When a flexible, relatively soft foam is used, the(H_(inner core center)) of the foam may have a Shore A hardness of about10 or greater, and preferably has a lower limit of 15, 18, 20, 25, 28,30, 35, 38, or 40 Shore A hardness and an upper limit of about 45 or 48,or 50, 54, 58, 60, 65, 70, 80, 85, or 90 Shore A hardness. In onepreferred embodiment, the (H_(inner core center)) of the foam is about55 Shore A.

The H_(inner core center), as measured in Shore D units, is about 15Shore D or greater and more preferably within a range having a lowerlimit of about 15 or 18 or 20 or 22 or 25 or 28 or 30 or 32 or 36 or 40or 44 Shore D and an upper limit of about 45 or 48 or 50 or 52 or 55 or58 or 60 or 62 or 64 or 66 or 70 or 72 or 74 or 78 or 80 or 82 or 84 or88 or 90 Shore D.

Meanwhile, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C, is preferably about 20Shore C or greater and may have, for example, a lower limit of about 10or 14 or 17 or 20 or 22 or 24 or 28 or 30 or 32 or 35 or 36 or 40 or 42or 44 or 48 or 50 Shore C and an upper limit of about 52 or 55 or 58 or60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or 86 or 88 or 90 or 92 or95 Shore C. When a flexible, relatively soft foam is used, the(H_(inner core surface)) of the foam may have a Shore A hardness ofabout 12 or greater, and preferably has a lower limit of 12, 16, 20, 24,26, 28, 30, 34, 40, 42, 46, or 50 Shore A hardness and an upper limit ofabout 52, 55, 58, 60, 62, 66, 70, 74, 78, 80, 84, 88, 90, or 95 Shore Ahardness. In one preferred embodiment, the (H_(inner core surface)) isabout 60 Shore A. The (H_(inner core surface)), as measured in Shore Dunits, preferably has a lower limit of about 25 or 28 or 30 or 32 or 36or 40 or 44 Shore D and an upper limit of about 45 or 48 or 50 or 52 or55 or 58 or 60 or 62 or 64 or 66 or 70 or 74 or 78 or 80 or 82 or 84 or88 or 90 or 94 or 96 Shore D.

Density of the Inner Core

The foamed inner core preferably has a specific gravity of about 0.20 toabout 1.00 g/cc. That is, the density of the inner core (as measured atany point of the inner core structure) is preferably within the range ofabout 0.20 to about 1.00 g/cc. By the term, “specific gravity of theinner core” (“SG_(inner)”), it is generally meant the specific gravityof the inner core as measured at any point of the inner core structure.It should be understood, however, that the specific gravity values, astaken at different particular points of the inner core structure, mayvary. For example, the foamed inner core may have a “positive” densitygradient (that is, the outer surface (skin) of the inner core may have adensity greater than the geometric center of the inner core.) In onepreferred version, the specific gravity of the geometric center of theinner core (SG_(center of inner core)) is less than 0.80 g/cc and morepreferably less than 0.70 g/cc. More particularly, in one version, the(SG_(center of inner core)) is in the range of about 0.10 to about 0.06g/cc. For example, the (SG_(center of inner core)) may be within a rangehaving a lower limit of about 0.10 or 0.15 of 0.20 or 0.24 or 0.30 or0.35 or 0.37 or 0.40 or 0.42 or 0.45 or 0.47 or 0.50 and an upper limitof about 0.60 or 0.65 or 0.70 or 0.74 or 0.78 or 0.80, or 0.82 or 0.84or 0.85 or 0.88 or 0.90 g/cc. Meanwhile, the specific gravity of theouter surface (skin) of the inner core (SG_(skin of inner core)), in onepreferred version, is greater than about 0.90 g/cc and more preferablygreater than 1.00 g/cc. For example, the (SG_(skin of inner core)) mayfall within the range of about 0.90 to about 1.25 g/cc. Moreparticularly, in one version, the (SG_(skin of inner core)) may have aspecific gravity with a lower limit of about 0.90 or 0.92 or 0.95 or0.98 or 1.00 or 1.02 or 1.06 or 1.10 g/cc and an upper limit of about1.12 or 1.15 or 1.18 or 1.20 or 1.24 or 1.30 or 1.32 or 1.35 g/cc. Inother instances, the outer skin may have a specific gravity of less than0.90 g/cc. For example, the specific gravity of the outer skin(SG_(skin of inner core)) may be about 0.75 or 0.80 or 0.82 or 0.85 or0.88 g/cc. In such instances, wherein both the(SG_(center of inner core)) and (SG_(skin of inner core)) are less than0.90 g/cc, it is still preferred that the (SG_(center of inner core)) beless than the (SG_(skin of inner core)).

Thermoset Materials

As discussed above, the inner core (center) is made preferably from afoamed polyurethane composition. Preferably, a two-layered or dual-coreis made, wherein the inner core is surrounded by an outer core layer. Inone preferred embodiment, the outer core layer is formed from anon-foamed thermoset composition and more preferably from a non-foamedthermoset rubber composition.

Suitable thermoset rubber materials that may be used to form the outercore layer include, but are not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber composition also may include filler(s) such as materialsselected from carbon black, clay and nanoclay particles as discussedabove, talc (e.g., Luzenac HAR® high aspect ratio talcs, commerciallyavailable from Luzenac America, Inc.), glass (e.g., glass flake, milledglass, and microglass), mica and mica-based pigments (e.g., Iriodin®pearl luster pigments, commercially available from The Merck Group), andcombinations thereof. Metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed. As discussedfurther below, in one preferred embodiment, the specific gravity of theinner core layer (for example, foamed polyurethane) has a specificgravity less than the outer core layer (for example, polybutadienerubber). In such an event, if mineral, metal, or other fillers are addedto the polybutadiene rubber composition used to form the outer core, itis important the concentration of such fillers be sufficient so that thespecific gravity of the outer core layer is greater than the specificgravity of the inner core. For example, the concentration of the fillersmay be in an amount of at least about 5% by weight based on total weightof composition

In addition, the rubber compositions may include antioxidants. Also,processing aids such as high molecular weight organic acids and saltsthereof may be added to the composition. Suitable organic acids arealiphatic organic acids, aromatic organic acids, saturatedmono-functional organic acids, unsaturated monofunctional organic acids,multi-unsaturated mono-functional organic acids, and dimerizedderivatives thereof. Particular examples of suitable organic acidsinclude, but are not limited to, caproic acid, caprylic acid, capricacid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid,linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylaceticacid, naphthalenoic acid, and dimerized derivatives thereof. The organicacids are aliphatic, mono-functional (saturated, unsaturated, ormulti-unsaturated) organic acids. Salts of these organic acids may alsobe employed. The salts of organic acids include the salts of barium,lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium,strontium, titanium, tungsten, magnesium, cesium, iron, nickel, silver,aluminum, tin, or calcium, salts of fatty acids, particularly stearic,behenic, erucic, oleic, linoelic or dimerized derivatives thereof. It ispreferred that the organic acids and salts of the present invention berelatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending.) Otheringredients such as accelerators (for example, tetra methylthiuram),processing aids, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, chemical blowing andfoaming agents, defoaming agents, stabilizers, softening agents, impactmodifiers, antiozonants, as well as other additives known in the art maybe added to the rubber composition.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; and DIENE 55NF, 70AC, and 320 AC, availablefrom Firestone Polymers of Akron, Ohio.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

Thermoplastic Materials

As discussed above, in one preferred embodiment, a thermoset rubbercomposition is used to form the outer core. In alternative embodiments,the outer core layer is made from a thermoplastic material, which ispreferably non-foamed, for example, a non-foamed ionomer composition.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers,wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturatedcarboxylic acid, and Y is a softening monomer. O is preferably selectedfrom ethylene and propylene. X is preferably selected from methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylic acid in the acid copolymer is typically from 1 wt. % to35 wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5wt. % to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,based on total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed in U.S.Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference. The acid copolymer can be reacted withthe optional high molecular weight organic acid and the cation sourcesimultaneously, or prior to the addition of the cation source. Suitablecation sources include, but are not limited to, metal ion sources, suchas compounds of alkali metals, alkaline earth metals, transition metals,and rare earth elements; ammonium salts and monoamine salts; andcombinations thereof. Preferred cation sources are compounds ofmagnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals. The amount of cation used in the composition is readilydetermined based on desired level of neutralization. As discussed above,for HNP compositions, the acid groups are neutralized to 70% or greater,preferably 70 to 100%, more preferably 90 to 100%. In one embodiment, anexcess amount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In other embodiments,partially-neutralized compositions are prepared, wherein 10% or greater,normally 30% or greater of the acid groups are neutralized. Whenaluminum is used as the cation source, it is preferably used at lowlevels with another cation such as zinc, sodium, or lithium, sincealuminum has a dramatic effect on melt flow reduction and cannot be usedalone at high levels. For example, aluminum is used to neutralize about10% of the acid groups and sodium is added to neutralize an additional90% of the acid groups.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin. Such ionicplasticizers are used to make conventional ionomer composition moreprocessable as described in Rajagopalan et al., U.S. Pat. No. 6,756,436,the disclosure of which is hereby incorporated by reference. In thepresent invention such ionic plasticizers are optional. In one preferredembodiment, a thermoplastic ionomer composition is made by neutralizingabout 70 wt % or more of the acid groups without the use of any ionicplasticizer. On the other hand, in some instances, it may be desirableto add a small amount of ionic plasticizer, provided that it does notadversely affect the heat-resistance properties of the composition. Forexample, the ionic plasticizer may be added in an amount of about 10 toabout 50 weight percent (wt. %) of the composition, more preferably 30to 55 wt. %.

The organic acids may be aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. Suitable fatty acid saltsinclude, for example, metal stearates, laureates, oleates, palmitates,pelargonates, and the like. For example, fatty acid salts such as zincstearate, calcium stearate, magnesium stearate, barium stearate, and thelike can be used. The salts of fatty acids are generally fatty acidsneutralized with metal ions. The metal cation salts provide the cationscapable of neutralizing (at varying levels) the carboxylic acid groupsof the fatty acids. Examples include the sulfate, carbonate, acetate andhydroxide salts of metals such as barium, lithium, sodium, zinc,bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, and blends thereof. It is preferred the organic acids and saltsbe relatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

Other suitable thermoplastic polymers that may be used to form the innercover layer include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof.)

(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof;

(b) polyamides, polyamide-ethers, and polyamide-esters, and thosedisclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, theentire disclosures of which are hereby incorporated herein by reference,and blends of two or more thereof;

(c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and blendsof two or more thereof;

(d) fluoropolymers, such as those disclosed in U.S. Pat. Nos. 5,691,066,6,747,110 and 7,009,002, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof;

(e) polystyrenes, such as poly(styrene-co-maleic anhydride),acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylenestyrene, and blends of two or more thereof;

(f) polyvinyl chlorides and grafted polyvinyl chlorides, and blends oftwo or more thereof;

(g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof;

(h) polyethers, such as polyarylene ethers, polyphenylene oxides, blockcopolymers of alkenyl aromatics with vinyl aromatics and polyamicesters,and blends of two or more thereof;

(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and

(j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the inner cover layers in accordance with thisinvention. For example, thermoplastic polyolefins such as linear lowdensity polyethylene (LLDPE), low density polyethylene (LDPE), and highdensity polyethylene (HDPE) may be cross-linked to form bonds betweenthe polymer chains. The cross-linked thermoplastic material typicallyhas improved physical properties and strength over non-cross-linkedthermoplastics, particularly at temperatures above the crystallinemelting point. Preferably a partially or fully-neutralized ionomer, asdescribed above, is covalently cross-linked to render it into athermoset composition (that is, it contains at least some level ofcovalent, irreversable cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

Modifications in the thermoplastic polymeric structure of thermoplasticscan be induced by a number of methods, including exposing thethermoplastic material to high-energy radiation or through a chemicalprocess using peroxide. Radiation sources include, but are not limitedto, gamma-rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms andallows for considerable depth of treatment, if necessary. For corelayers requiring lower depth of penetration, electron-beam acceleratorsor UV and IR light sources can be used. Useful UV and IR irradiationmethods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, whichare incorporated herein by reference. The thermoplastic core layers maybe irradiated at dosages greater than 0.05 Mrd, preferably ranging from1 Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and mostpreferably from 4 Mrd to 10 Mrd. In one preferred embodiment, the coresare irradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered structure comprising an inner core andouter core layer. Referring to FIG. 4, one version of a four-piece golfball that can be made in accordance with this invention is generallyindicated at (20). The ball (20) contains an inner core (center) (22)and surrounding outer core layer (24). The dual-core sub-assembly isencased by a multi-layered cover comprising an inner cover (26) andouter cover (28). The inner core (22) is relatively small in volume andgenerally has a diameter within a range of about 0.10 to about 1.10inches. More particularly, the inner core (22) preferably has a diametersize with a lower limit of about 0.15 or 0.25 or 0.35 or 0.45 or 0.55inches and an upper limit of about 0.60 or 0.70 or 0.80 or 0.90 inches.In one preferred version, the diameter of the inner core (22) is in therange of about 0.025 to about 0.080 inches, more preferably about 0.030to about 0.075 inches. Meanwhile, the outer core layer (24) generallyhas a thickness within a range of about 0.010 to about 0.250 inches andpreferably has a lower limit of 0.010 or 0.020 or 0.025 or 0.030 inchesand an upper limit of 0.070 or 0.080 or 0.100 or 0.200 inches. In onepreferred version, the outer core layer has a thickness in the range ofabout 0.040 to about 0.170 inches, more preferably about 0.060 to about0.150 inches.

Referring to FIG. 5, in another version, a three-piece golf ball (30)contains an inner core (center) (32) and outer core layer (34). Thedual-core sub-assembly is surrounded by a single-layered cover (36).

The hardness of the core sub-assembly (inner core and outer core layer)is an important property. In general, cores with relatively highhardness values have higher compression and tend to have good durabilityand resiliency. However, some high compression balls are stiff and thismay have a detrimental effect on shot control and placement. Thus, theoptimum balance of hardness in the core sub-assembly needs to beattained.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C. In a secondalternative version, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another embodiment, both the inner core andouter core layers have zero or negative hardness gradients.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the outer core layer has a greater hardness value thanthe inner surface of the outer core layer, the given outer core layerwill be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the outer core layer has a lesser hardness valuethan the inner surface of the outer core layer, the given outer corelayer will be considered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 5 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 5 to about 88 ShoreD and more particularly within a range having a lower limit of about 5or 10 or 18 or 20 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50 or 52Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or68 or 70 or 74 or 76 or 80 or 82 or 84 or 88 Shore D. In anotherexample, the center hardness of the inner core (H_(inner core center)),as measured in Shore C units, is preferably about 10 Shore C or greater;for example, the H_(inner core center) may have a lower limit of about10 or 14 or 16 or 20 or 23 or 24 or 28 or 31 or 34 or 37 or 40 or 44Shore C and an upper limit of about 46 or 48 or 50 or 51 or 53 or 55 or58 or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80 or 84 or90 Shore C. Concerning the outer surface hardness of the inner core(H_(inner core surface)), this hardness is preferably about 12 Shore Dor greater; for example, the H_(inner core surface) may fall within arange having a lower limit of about 12 or 15 or 18 or 20 or 22 or 26 or30 or 34 or 36 or 38 or 42 or 48 or 50 or 52 Shore D and an upper limitof about 54 or 56 or 58 or 60 or 62 or 70 or 72 or 75 or 78 or 80 or 82or 84 or 86 or 90 Shore D. In one version, the outer surface hardness ofthe inner core (H_(inner core surface)), as measured in Shore C units,has a lower limit of about 13 or 15 or 18 or 20 or 22 or 24 or 27 or 28or 30 or 32 or 34 or 38 or 44 or 47 or 48 Shore C and an upper limit ofabout 50 or 54 or 56 or 61 or 65 or 66 or 68 or 70 or 73 or 76 or 78 or80 or 84 or 86 or 88 or 90 or 92 Shore C. In another version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 10 Shore C to about 50 Shore C; and the outer surface hardness ofthe inner core (R_(inner core surface)) is in the range of about 5 ShoreC to about 50 Shore C.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 40 Shore D or greater, andmore preferably within a range having a lower limit of about 40 or 42 or44 or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or60 or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90Shore D. The outer surface hardness of the outer core layer(H_(outer surface of OC)), as measured in Shore C units, preferably hasa lower limit of about 40 or 42 or 45 or 48 or 50 or 54 or 58 or 60 or63 or 65 or 67 or 720 or 72 or 73 or 76 Shore C, and an upper limit ofabout 78 or 80 or 84 or 87 or 88 or 89 or 90 or 92 or 95 Shore C. And,the inner surface of the outer core layer (R_(inner surface of OC)) ormidpoint hardness of the outer core layer (H_(midpoint of OC)),preferably has a hardness of about 40 Shore D or greater, and morepreferably within a range having a lower limit of about 40 or 42 or 44or 46 or 48 or 50 or 52 and an upper limit of about 54 or 56 or 58 or 60or 62 or 64 or 70 or 74 or 78 or 80 or 82 or 85 or 87 or 88 or 90 ShoreD. The inner surface hardness (H_(inner surface of OC)) or midpointhardness (H_(midpoint of OC)) of the outer core layer, as measured inShore C units, preferably has a lower limit of about 40 or 42 or 44 or45 or 47 or 50 or 52 or 54 or 55 or 58 or 60 or 63 or 65 or 67 or 70 or73 or 75 Shore C, and an upper limit of about 78 or 80 or 85 or 88 or 89or 90 or 92 or 95 Shore C. Likewise, the midpoint of a core layer istaken at a point equidistant from the inner surface and outer surface ofthe layer to be measured, most typically an outer core layer. Once oneor more core layers surround a layer of interest, the exact midpoint maybe difficult to determine, therefore, for the purposes of the presentinvention, the measurement of “midpoint” hardness of a layer is takenwithin plus or minus 1 mm of the measured midpoint of the layer.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is less than the outer surface hardness(H_(inner core surface)) or midpoint hardness (H_(midpoint of OC)), ofthe inner core by at least 3 Shore C units and more preferably by atleast 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the inner core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

As discussed above, the inner core is preferably formed from a foamedthermoplastic or thermoset composition and more preferably foamedpolyurethanes. And, the outer core layer is formed preferably from anon-foamed thermoset composition such as polybutadiene rubber. The outercore layer also may be formed from non-foamed thermoplasticcompositions.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 10 Shore C to about 60 Shore C, preferably about 13 Shore C toabout 55 Shore C; and the (H_(outer surface of OC)) is in the range ofabout 65 to about 96 Shore C, preferably about 68 Shore C to about 94Shore C or about 75 Shore C to about 93 Shore C, to provide a positivehardness gradient across the core assembly. The gradient across the coreassembly will vary based on several factors including, but not limitedto, the dimensions of the inner core, intermediate core, and outer corelayers.

The inner core preferably has a diameter in the range of about 0.100 toabout 1.100 inches. For example, the inner core may have a diameterwithin a range of about 0.100 to about 0.500 inches. In another example,the inner core may have a diameter within a range of about 0.300 toabout 0.800 inches. More particularly, the inner core may have adiameter size with a lower limit of about 0.10 or 0.12 or 0.15 or 0.25or 0.30 or 0.35 or 0.45 or 0.55 inches and an upper limit of about 0.60or 0.65 or 0.70 or 0.80 or 0.90 or 1.00 or 1.10 inches. As far as theouter core layer is concerned, it preferably has a thickness in therange of about 0.100 to about 0.750 inches. For example, the lower limitof thickness may be about 0.050 or 0.100 or 0.150 or 0.200 or 0.250 or0.300 or 0.340 or 0.400 and the upper limit may be about 0.500 or 0.550or 0.600 or 0.650 or 0.700 or 0.750 inches.

Dimensions—Thickness and Volume

Dual-layered core structures containing layers with various thicknessand volume levels may be made in accordance with this invention. Forexample, in one version, the total diameter of the core structure is0.20 inches and the total volume of the core structure is 0.23 cc. Moreparticularly, in this example, the diameter of the inner core is 0.10inches and the volume of the inner core is 0.10 cc; while the thicknessof the outer core is 0.100 inches and the volume of the outer core is0.13 cc. In another version, the total core diameter is about 1.55inches and the total core volume is 31.96 cc. In this version, the outercore layer has a thickness of 0.400 inches and volume of 28.34 cc.Meanwhile, the inner core has a diameter of 0.75 inches and volume of3.62 cm. In one embodiment, the volume of the outer core layer isgreater than the volume of the inner core. In another embodiment, thevolume of the outer core layer and inner core are equivalent. In stillanother embodiment, the volume of the outer core layer is less than thevolume of the inner core. Other examples of core structures containinglayers of varying thicknesses and volumes are described below in TableA.

TABLE A Sample Core Dimensions Thermoset Foamed Total Core Total CoreOuter Core Outer Core Inner Core Volume of Example Diameter VolumeThickness Volume Diameter Inner Core A 0.30″  0.23 cc 0.100″  0.13 cc0.10″ 0.10 cc B 1.60″ 33.15 cc 0.750″ 33.05 cc 0.10″ 0.10 cc C 1.55″31.96 cc 0.225″ 11.42 cc 1.10″ 11.42 cc  D 1.55″ 31.96 cc 0.400″ 28.34cc 0.75″ 3.62 cc E 1.55″ 31.96 cc 0.525″ 28.34 cc 0.50″ 3.62 cc

In one preferred embodiment, the inner core has a specific gravity inthe range of about 0.25 to about 1.25 g/cc. Also, as discussed above,the specific gravity of the inner core may vary at different points ofthe inner core structure. That is, there may be a specific gravitygradient in the inner core. For example, in one preferred version, thegeometric center of the inner core has a density in the range of about0.25 to about 0.75 g/cc; while the outer skin of the inner core has adensity in the range of about 0.75 to about 1.50 g/cc.

Meanwhile, the outer core layer preferably has a relatively highspecific gravity. Thus, the specific gravity of the inner core layer(SG_(inner)) is preferably less than the specific gravity of the outercore layer (SG_(outer)) By the term, “specific gravity of the outer corelayer” (“SG_(outer)”), it is generally meant the specific gravity of theouter core layer as measured at any point of the outer core layer. Thespecific gravity values at different points in the outer core layer mayvary. That is, there may be specific gravity gradients in the outer corelayer similar to the inner core. For example, the outer core layer mayhave a specific gravity within a range having a lower limit of about0.50 or 0.60 or 0.70 or 0.75 or 0.85 or 0.95 or 1.00 or 1.10 or 1.25 or1.30 or 1.36 or 1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or 1.75 or2.00 and an upper limit of 2.50 or 2.60 or 2.80 or 2.90 or 3.00 or 3.10or 3.25 or 3.50 or 3.60 or 3.80 or 4.00, 4.25 or 5.00 or 5.10 or 5.20 or5.30 or 5.40 or 6.00 or 6.20 or 6.25 or 6.30 or 6.40 or 6.50 or 7.00 or7.10 or 7.25 or 7.50 or 7.60 or 7.65 or 7.80 or 8.00 or 8.20 or 8.50 or9.00 or 9.75 or 10.00 g/cc.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center (the center piece(for example, inner core) has a higher specific gravity than the outerpiece (for example, outer core layers), less force is required to changeits rotational rate, and the ball has a relatively low Moment ofInertia. In such balls, most of the mass is located close to the ball'saxis of rotation and less force is needed to generate spin. Thus, theball has a generally high spin rate as the ball leaves the club's faceafter making impact. Conversely, if the ball's mass is concentratedtowards the outer surface (the outer piece (for example, outer corelayers) has a higher specific gravity than the center piece (forexample, inner core), more force is required to change its rotationalrate, and the ball has a relatively high Moment of Inertia. That is, insuch balls, most of the mass is located away from the ball's axis ofrotation and more force is needed to generate spin. Such balls have agenerally low spin rate as the ball leaves the club's face after makingimpact.

More particularly, as described in Sullivan, U.S. Pat. No. 6,494,795 andLadd et al., U.S. Pat. No. 7,651,415, the formula for the Moment ofInertia for a sphere through any diameter is given in the CRC StandardMathematical Tables, 24th Edition, 1976 at 20 (hereinafter CRCreference). The term, “specific gravity” as used herein, has itsordinary and customary meaning, that is, the ratio of the density of asubstance to the density of water at 4° C., and the density of water atthis temperature is 1 g/cm³.

In one embodiment, the golf balls of this invention are relatively lowspin and long distance. That is, the foam core construction, asdescribed above, wherein the inner core is made of a foamed compositionhelps provide a relatively low spin ball having good resiliency. Theinner foam cores of this invention preferably have a Coefficient ofRestitution (COR) of about 0.300 or greater; more preferably about 0.400or greater, and even more preferably about 0.450 or greater. Theresulting balls containing the dual-layered core constructions of thisinvention and cover of at least one layer preferably have a COR of about0.700 or greater, more preferably about 0.730 or greater; and even morepreferably about 0.750 to 0.810 or greater. The inner foam corespreferably have a Soft Center Deflection Index (“SCDI”) compression, asdescribed in the Test Methods below, in the range of about 50 to about190, and more preferably in the range of about 60 to about 170.

The USGA has established a maximum weight of 45.93 g (1.62 ounces) forgolf balls. For play outside of USGA rules, the golf balls can beheavier. In one preferred embodiment, the weight of the multi-layeredcore is in the range of about 28 to about 38 grams. Also, golf ballsmade in accordance with this invention can be of any size, although theUSGA requires that golf balls used in competition have a diameter of atleast 1.68 inches. For play outside of United States Golf Association(USGA) rules, the golf balls can be of a smaller size. Normally, golfballs are manufactured in accordance with USGA requirements and have adiameter in the range of about 1.68 to about 1.80 inches. As discussedfurther below, the golf ball contains a cover which may be multi-layeredand in addition may contain intermediate (casing) layers, and thethickness levels of these layers also must be considered. Thus, ingeneral, the dual-layer core structure normally has an overall diameterwithin a range having a lower limit of about 1.00 or 1.20 or 1.30 or1.40 inches and an upper limit of about 1.58 or 1.60 or 1.62 or 1.66inches, and more preferably in the range of about 1.3 to 1.65 inches. Inone embodiment, the diameter of the core sub-assembly is in the range ofabout 1.45 to about 1.62 inches.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball sub-assembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball sub-assembly includes the core structure and one or morecasing (mantle) layers disposed about the core. In one particularlypreferred version, the golf ball includes a multi-layered covercomprising inner and outer cover layers. The inner cover layer ispreferably formed from a composition comprising an ionomer or a blend oftwo or more ionomers that helps impart hardness to the ball. In aparticular embodiment, the inner cover layer is formed from acomposition comprising a high acid ionomer. A particularly suitable highacid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer ofethylene and methacrylic acid, having an acid content of 19 wt %, whichis 45% neutralized with sodium. In another particular embodiment, theinner cover layer is formed from a composition comprising a high acidionomer and a maleic anhydride-grafted non-ionomeric polymer. Aparticularly suitable maleic anhydride-grafted polymer is Fusabond 525D®(DuPont). Fusabond 525D® is a maleic anhydride-grafted,metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt %maleic anhydride grafted onto the copolymer. A particularly preferredblend of high acid ionomer and maleic anhydride-grafted polymer is an 84wt %/16 wt % blend of Surlyn 8150® and Fusabond 525D®. Blends of highacid ionomers with maleic anhydride-grafted polymers are furtherdisclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, theentire disclosures of which are hereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® IOionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The compositions used to make the casing (mantle) and cover layers maycontain a wide variety of fillers and additives to impart specificproperties to the ball. For example, relatively heavy-weight andlight-weight metal fillers such as, particulate; powders; flakes; andfibers of copper, steel, brass, tungsten, titanium, aluminum, magnesium,molybdenum, cobalt, nickel, iron, lead, tin, zinc, barium, bismuth,bronze, silver, gold, and platinum, and alloys and combinations thereofmay be used to adjust the specific gravity of the ball. Other additivesand fillers include, but are not limited to, optical brighteners,coloring agents, fluorescent agents, whitening agents, UV absorbers,light stabilizers, surfactants, processing aids, antioxidants,stabilizers, softening agents, fragrance components, plasticizers,impact modifiers, titanium dioxide, clay, mica, talc, glass flakes,milled glass, and mixtures thereof.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the intermediate layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

A single cover or, preferably, an inner cover layer is formed around theouter core layer. When an inner cover layer is present, an outer coverlayer is formed over the inner cover layer. Most preferably, the innercover is formed from an ionomeric material and the outer cover layer isformed from a polyurethane material, and the outer cover layer has ahardness that is less than that of the inner cover layer. Preferably,the inner cover has a hardness of greater than about 60 Shore D and theouter cover layer has a hardness of less than about 60 Shore D. In analternative embodiment, the inner cover layer is comprised of apartially or fully neutralized ionomer, a thermoplastic polyesterelastomer such as Hytrel™, commercially available form DuPont, athermoplastic polyether block amide, such as Pebax™, commerciallyavailable from Arkema, Inc., or a thermoplastic or thermosettingpolyurethane or polyurea, and the outer cover layer is comprised of anionomeric material. In this alternative embodiment, the inner coverlayer has a hardness of less than about 60 Shore D and the outer coverlayer has a hardness of greater than about 55 Shore D and the innercover layer hardness is less than the outer cover layer hardness.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Manufacturing of Golf Balls

As described above, the inner core preferably is formed by molding afoamed composition containing secondary heat-activated blowing agents.The outer core layer, which surrounds the inner core, is formed bymolding a composition over the inner core. Then, the casing and/or coverlayers are applied over the core sub-assembly. Prior to this step, thecore structure may be surface-treated to increase the adhesion betweenits outer surface and the next layer that will be applied over the core.Such surface-treatment may include mechanically or chemically-abradingthe outer surface of the core. For example, the core may be subjected tocorona-discharge, plasma-treatment, silane-dipping, or other treatmentmethods known to those in the art.

The cover layers are formed over the core or ball sub-assembly (the corestructure and any casing layers disposed about the core) using asuitable technique such as, for example, compression-molding,flip-molding, injection-molding, retractable pin injection-molding,reaction injection-molding (RIM), liquid injection-molding, casting,spraying, powder-coating, vacuum-forming, flow-coating, dipping,spin-coating, and the like. Preferably, each cover layer is separatelyformed over the ball subassembly. For example, an ethylene acidcopolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the core sub-assembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the sub-assembly.In another method, the ionomer composition is injection-molded directlyonto the core sub-assembly using retractable pin injection molding. Anouter cover layer comprising a polyurethane or polyurea composition overthe ball sub-assembly may be formed by using a casting process.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball. In FIG. 6, a finished golf ball(38) having a dimpled outer cover (40) made in accordance with thepresent invention is shown. As discussed above, various patterns andgeometric shapes of the dimples (40) can be used to modify theaerodynamic properties of the golf ball.

Different ball constructions can be made using the methods and coreconstructions of this invention as shown in FIGS. 1-6. Such golf ballconstructions include, for example, five-piece, and six-piececonstructions. It should be understood that the golf ball components andfinished golf balls shown in FIGS. 1-6 are for illustrative purposesonly, and they are not meant to be restrictive. Other golf ballconstructions can be made in accordance with this invention. Forexample, the foam composition of this invention is primarily discussedherein as being suitable for producing a foam inner core or center for agolf ball. However, it is recognized that this foam composition may beused for producing an outer core layer, casing layer, cover, or anyother suitable component layer for the golf ball in accordance with thisinvention.

Cores Having Three Layers

In another example, multi-layered cores having an inner core,intermediate core layer, and outer core layer, wherein the intermediatecore layer is disposed between the intermediate and outer core layersmay be prepared in accordance with this invention. More particularly, asdiscussed above, the inner core may be constructed from a foamedcomposition, preferably foamed polyurethane. Meanwhile, the intermediateand outer core layers may be formed from non-foamed thermoset orthermoplastic materials. Suitable thermoset and thermoplasticcompositions that may be used to form the intermediate/outer core layersare discussed above. For example, each of the intermediate and outercore layers may be formed from a thermoset rubber composition. Thus, theintermediate core layer may be formed from a first thermoset rubbercomposition; and the outer core layer may be formed from a secondthermoset rubber composition. In another embodiment, the intermediatecore layer is formed from a non-foamed thermoset composition; and theouter core layer is formed from a non-foamed thermoplastic composition.In a third embodiment, the intermediate core layer is formed from anon-foamed thermoplastic composition; and the outer core layer is formedfrom a non-foamed thermoset composition. Finally, in a fourthembodiment, the intermediate core layer is formed from a firstnon-foamed thermoplastic composition; and the outer core layer is formedfrom a second non-foamed thermoplastic compositions.

The above-discussed thermoset and thermoplastic compositions may be usedto form the intermediate and outer core layers. In one embodiment, thespecific gravity of the inner core (foamed composition) is less than thespecific gravity of the intermediate and outer core layers. The specificgravities of the intermediate and outer core layers may be the same ordifferent. In one version, the specific gravity of the intermediate corelayer is greater than the specific gravity of the outer core layer. Inanother version, the specific gravity of the outer core is greater thanthe specific gravity of the intermediate core layer.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used. Likewise,the midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. Once again, once one or more core layerssurround a layer of interest, the exact midpoint may be difficult todetermine, therefore, for the purposes of the present invention, themeasurement of “midpoint” hardness of a layer is taken within plus orminus 1 mm of the measured midpoint of the layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dhardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Density.

The density refers to the weight per unit volume (typically, g/cm³) ofthe material and can be measured per ASTM D-1622.

It is understood that the golf ball compositions, constructions, andproducts described and illustrated herein represent only someembodiments of the invention. It is appreciated by those skilled in theart that various changes and additions can be made to compositions,constructions, and products without departing from the spirit and scopeof this invention. It is intended that all such embodiments be coveredby the appended claims.

We claim:
 1. A method for producing a core assembly for a golf ball,comprising the steps of: i) introducing a polyurethane compositioncomprising a primary blowing agent and secondary blowing agent into amold for preparing a spherical inner core; ii) heating the polyurethanecomposition so that the primary blowing agent, and not the secondaryblowing agent, is activated and foaming of the composition is initiated;iii) molding a rubber composition over the foamed polyurethanecomposition so that the secondary blowing agent is activated and thepolyurethane composition is further foamed to produce a core assemblyhaving a fully foamed polyurethane inner core and an overlying rubberouter core layer.
 2. The method of claim 1, wherein the primary blowingagent is water and the secondary blowing agent is selected from thegroup consisting of azo, nitroso, hydrazine, carbazide, and hydrogencarbonate compounds, and mixtures thereof.
 3. The method of claim 1,wherein the secondary blowing agent is selected from the groupconsisting of 4,4′-oxybis(benzenesulfonylhydrazide) and sodium hydrogencarbonate.
 4. The method of claim 1, wherein the foamed polyurethanecomposition is prepared by adding water and a secondary chemical blowingagent to a mixture of polyisocyanate, polyol, and curing agentcompounds, surfactant, and catalyst, the water being added in asufficient amount to cause the mixture to foam.
 5. The method of claim1, wherein the outer core layer comprises at least one thermoset rubbermaterial selected from the group consisting of polybutadiene,ethylene-propylene rubber, ethylene-propylene-diene rubber,polyisoprene, styrene-butadiene rubber, polyalkenamers, butyl rubber,halobutyl rubber, polystyrene elastomers, copolymers of isobutylene andp-alkylstyrene, halogenated copolymers of isobutylene andp-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and mixtures thereof
 6. Themethod of claim 5, wherein the outer core layer comprises a thermosetpolybutadiene rubber composition.
 7. The method of claim 1, wherein theinner core has a specific gravity (SG_(inner)) and a center hardness(H_(inner core center)) and the outer core layer has a specific gravity(SG_(outer)) and an outer surface hardness (H_(outer surface of OC)),wherein the SG_(outer), is greater than the SG_(inner), and theH_(inner core center) is in the range of about 10 to about 60 Shore Cand the H_(outer surface of OC) is in the range of about 65 to about 96Shore C to provide a positive hardness gradient across the coreassembly.
 8. The method of claim 1, wherein the inner core has adiameter in the range of about 0.100 to about 0.900 inches and aspecific gravity in the range of about 0.25 to about 1.25 g/cc.
 9. Themethod of claim 1, wherein the inner core has a diameter in the range ofabout 0.400 to about 0.800 inches and a specific gravity in the range ofabout 0.30 to about 0.95 g/cc.
 10. The method of claim 1, wherein theouter core layer has a thickness in the range of about 0.250 to about0.750 inches and a specific gravity in the range of about 0.60 to about2.90 g/cc.
 11. The method of claim 1, wherein the inner core layer hasan outer surface hardness (H_(inner core surface)) and a center hardness(H_(inner core center)), the H_(inner core surface) being greater thanthe H_(inner core center) to provide a positive hardness gradient; andthe outer core layer has an outer surface hardness(H_(outer surface of OC)) and a midpoint hardness (H_(midpoint of OC)),the H_(outer surface of OC) being greater than the (H_(midpoint of OC)),to provide a positive hardness gradient.
 12. The method of claim 11,wherein the H_(inner core center) is in the range of about 10 to about48 Shore C and the H_(inner core surface) is in the range of about 24 toabout 55 Shore C.
 13. The method of claim 11, wherein theH_(inner core center) is in the range of about 15 to about 80 Shore Aand the H_(inner core surface) is in the range of about 20 to about 95Shore A.
 14. The golf ball of claim 11, wherein the H_(midpoint of OC)is in the range of about 40 to about 87 Shore C and theH_(outer surface of OC) is in the range of about 72 to about 95 Shore C.